Known weapon delivery systems to aid a pilot in shooting an enemy target in air-to-air or air-to-ground combat usually incorporate computers for solving fire control equations. The computer is normally fed with air data information including velocity, angle of attack, and side slip angle. In addition, an inertial system provides inertial attitude and accelerations. Also, by the use of radar, the range and angular direction of a target are fed to the computer. The computer generates a firing pipper which is displayed in a position to be observed by the pilot in his line of sight when chasing an enemy aircraft and by utilizing the firing pipper as a guide, the pilot attempts to position the aircraft fuselage in the proper firing direction.
Generally, the foregoing systems are of two general types. The first type is referred to as the "disturbed reticle sight" in which a lead angle is computed based on target range measurement by the radar system, and a rate gyro system that measures body angular rates. The principal disadvantage of this type of system is the oscillatory effect that results due to the equations that must be used. In addition, the pilot must estimate the range rate and use it to "lead" the target with the reticle beyond the computed lead angle.
The second type is referred to as the "director sight" in which not only range, but range rate is measured by a radar sensor and a line-of-sight tracker is used to obtain the target aircraft's relative location in space. An inertial platform is used to obtain the attacking aircraft's location and motions in space. The computations which involve the attacking aircraft's position and the target or enemy aircraft relative position, are used to generate a symbol which should fall directly on the target. The pilot needs to fly the aircraft to keep the symbol in his sight area. He may then fire his weapon whenever the symbol is on the target. The disadvantage of this system is the requirement for the line-of-sight tracker and the radar sensor which are subject to noise and jamming. Also, it cannot be used in air-to-ground weapon delivery since a ground target cannot be so easily distinguished from background in the tracker and radar return.
A major problem in all types of prior art weapon delivery systems in which a display is provided for the pilot resides in the lag time (referred to as "settling time") inherent when the pilot moves his controls and the aircraft is actually maneuvered to the new position in response to the command signals from the controls. The situation is particularly aggravated in air-to-air combat wherein the pilot attempts to place a tracking symbol on his display on the enemy aircraft. By way of example, if the enemy aircraft appears in the upper right hand portion of the display and the tracking symbol which may be a firing pipper, gun line, or other symbol to be superimposed on the target is elsewhere on the display, the pilot will move his controls to maneuver the aircraft such that its fuselage will point upwardly and to the right to effect the desired registration. However, movement of the controls by the pilot is translated into electrical signals which pass into the computer, portions of the computer in turn interpreting these signals and passing them to the flight control surfaces to actually physically move the flight control surfaces in a manner to cause the entire aircraft to assume the desired position. The time lag taken for the aircraft to assume the position commanded by the pilot is of such length that when the maneuver is completed the target is no longer at the originally observed location and thus a further correction must be made by the pilot and a further lag time is involved for the actual physical positioning of the aircraft to take place.
The net result of all the foregoing is an "oscillation" effect which occurs not only through the feedback of the pilot's senses but also in the fire control equations solved by the computer.
In summary, with present systems, it is difficult to align a symbol on the display on a rapidly moving enemy aircraft, wherein such alignment relies on a proper positioning of the entire aircraft fuselage, without the aforementioned lag time.